Welcome.

Good age for establishing your atheism.  I'm probably somewhere in that ballpark, myself.  I have vague memories of kindergarten Sunday school, thinking that all these stories they were telling us weren't any more believable than the Brothers Grimm stories that I had been told.  I came out of the closet to my parents when I was 14.  The solidification of my lack of belief probably happened more towards the kindergarten end of things, but it's hard to remember that far back, in detail.

Which denomination did you break out of?  I was raised Catholic ... was even an altar boy, from a pure desire to have something to do during mass.  If I had known about the dodgy priests, at the time, I might have reconsidered.